Organo-metallic zirconium catalysts for the preparation of polyesters



John R. Caldwell and John W. Wellman, Kingsport, Tenn., assignors to Eastman Kodak Company, Roch ester, N. Y., .a corporation of New Jersey 1 No Drawing. Application October 1952, Serial No. 313,074 t t t 1 13 Claims. .(Cl. 260-1-75) This invention relates to a process for ,preparing polyesters which comprisescond ensing a diester of a dicarboxylic acid with a polyhydroxy compound inthe presence of at leastone of a group of novel catalytic condensing agents which are alkali metal "and alkaline earth metal salts containing a complex zirconiumhexalkoxide radical and which are defined hereinbelow. These novel catalytic condensing agents can be advantageously employed in the preparation of t linearpolyesters wherein the dicarboxylic acid is an aromatic compound which does not contain any ethylenic (olefinic) unsaturation and the polyhydroxy compound is a dihydroxy compound. In preparing such linear polyesters it is advantageous to conduct the condensation in an inert atmosphere at an elevated temperature whichis increased during the course of the condensation up to a temperature of from about 225 to about 310 C., the condensation being conducted during the latter stages thereof at a very low subatmospheric pressure.

This application contains subjectmatter disclosed to some extent in a copending application, Serial No. 143,594, filed Feb. 10, 1'95 0,by J. R.Caldwell, now U. S. Patent No. 2,614,120, dated October 14,4952. This application also contains subject matter disclosed in other copending applications filed oneven date herewith by J. R. Caldwell, Serial Nos. 313,061 through 313,071.

Various polyesters of dicarboxylic acids and polyhydroxy compounds are .well known inthe prior ,art and have been used, for example, in the manufacture of paints and varnishes. Moreover, prior art disclosures set forth variouslinear condensation polyesters derived from dihydroxy compounds and dibasic acids such. as terephthalic acid which are capable of being drawn into fibers showing by characteristic X-ray patterns, orientation along the fiber axis. However, many of these linear polyesters possess .a relatively low meltingpoint and a fairly considerable solubility in varioussolvents whereby they are of restricted utility, especiallyin the textile field. These polyesters vary considerably in their characteristics, depending on the particular dicarboxylic acid and the particular polyhydroxy compound employed. Generally speaking, these polyesters have vari: ous physical characteristics which are not as satisfactory as could be desired.

The preparation .of polyesters .-is well known in the pn'or art and involves .the reaction of 3a di-basic dicar boxylic acid with a dihydric or polyhydric alcohol. It is advantageous .to employ. esters :of the dicarboxylic acid whereby ester interchange .takes place with the glycol or polyhydric alcohol to formia polyester and an alcohol. When using the .ester interchange .method, .thetime required to formthe .polyesters .is generally considerably less than when .the zfreedicarboxylic. acidsis employed. Thelong chain in the polyester is builtzupby aseries tof ester interchange reactions wherein the ,glycol displaces a relatively low-boilingialcohol component .of .the acid ester to form a glycol ester. During the last stages of the reaction, it is generally desirable to heat thecon- 2,720,504 Patented Oct. 11, 1955 ICC ; position or degradation of the polyester at these high temperatures.

In accordance with this invention, it has been found that certain compounds are especially valuable for use as catalytic condensing agents in the preparation of high melting linear polyesters. They have the. generalfformula structures set forth below:

wherein M is an alkali metal, e. g. lithium, sodium, or

' potassium, M is an alkaline earth metal such as Mg, Ca

' the alcohol solution.

These novel catalysts can be advantageously employed in' processes for preparing polyesters, which processes are described below. These novel catalysts are eflieetive only when substantially anhydrous conditions are employed and no free acid is present to a suficiently Slgnificant extent to destroy the catalyst compound; thus, when free acids are employed the acids are first reacted with a hydroxy compound (preferably the polyhydroxy compound to be employed in the polyesterification process) before the novel catalyst of this invention'is added.

The novel bimetallic alkoxide catalysts can be made as described by Meerwein, Ann. 455,227 (1927); 476,113 (-1929), viz. zirconium tetrachloride is treated with sodium alkoxide to give Zr(OR) 4 in excess alcohol; the alkali metal or alkaline earth metal is then dis'sol-yed in Alternatively, a solution of zir conium alkoxide can be mixed with a solution of the alkali metal or alkaline earth metal alkoxide in the calculated proportions.

As shown by Meerwein, these catalyst are not merely mixtures of the two metallic alkoxides. They are definite compounds having a salt-like structure. The Zirconium alkoxide coordinates 2 mols of alcohol to form an acid as follows:

This acid can then be reacted with a suitable, alkali metal, alkaline earth metal or an alkoxide thereof, e. g. sodium alkoxide, to give an acid salt having the structure:

The acid salt can react with another mol of alkali metal alkoxide to form a neutral salt according to the equation:

These salts are much more eliective as catalysts thaneither of themetal alkoxides used alone. Although the neutral salt, containing 2 atoms of alkali metal, is an efficient catalyst, the acid salt is usuallyto be preferredbecause ittends to be more stable under the conditionsof .the reaction.

The novel catalysts of this invention give a very rapid reaction rate at all stages of the polyesterification process, including the final step where the molecular weight is built up. They are particularly valuable for the preparation of high melting polyesters from 1,6 hexanediol and ester interchange reaction between a dicarboxylic acid ester and a glycol or glycol ester. The catalysts are especially valuable for the preparation of polyesters that melt above about 240 C., as for example, polyethylene terephthalate. The process of the invention is applicable to all of the polyesters described herein.

By employing the novel catalysts of this invention, the reaction rate of the polyesterification process can be increased by a factor which is generally from about 2 to 5 times the reaction rate obtainable when catalysts known in the prior art are employed. Moreover, the novel catalysts of this invention have the valuable characteristic of minimizing side reactions which have the tendency of causing considerable degradation of the polyester products at the relatively high temperatures employed in preparing highly polymeric polyesters. Furthermore, by employing these novel catalysts to increase the rate of condensation, the time available for possible decomposition of the high molecular weight polyester molecules being formed 1 at high temperatures is aprpeciably reduced. Thus, by

increasing the reaction rate, the time required to make a polyester is reduced which is quite important because at 250-300 C. the degree of color formation and extent of deleterious side reactions is proportional to the time of heating.

The polyesters produced when employing these novel catalysts have greatly improved properties as compared to products obtained employing catalysts known in the prior art. The molecular weight is considerably higher whereby highly polymeric polyesters are obtained. The color of the polyesters obtained is excellent; the products can therefore be employed for purposes calling for white or colorless materials. The physical properties of the polyesters obtained are also superior. At high temperatures there is a great improvement in the inherent viscosities of linear polyesters which are suitable for melt spinning or extrusion whereby fibers, films, etc. can be produced having properties superior to those obtainable with known catalysts.

The herein described novel catalysts are especially valuable for the preparation of polyesters employing diesters of p,p'-s ulfonyl dibenzoic acid as described in copending applications filed on even date herewith by J. R. Caldwell, Serial Nos. 313,061-313,068. Many of these polyesters are very high melting and the reaction must often be carried out at a temperature of 280-300f C. or higher. It has been found that relatively few catalysts are eifective at this temperature'other than those described in this application.

f It is an object of this invention to provide new and improved catalytic condensing agents for promoting the formation of improved polyesters in processes involving ester interchange and alcoholysis. A further object of this invention is to provide a new and improved method for the preparation of polyesters wherein such new and improved catalysts are employed. Other objects will become apparent elsewhere in this specification.

A broad aspect of this invention relates to a process for preparing a polyester which comprises condensing under substantially anhydrous conditions at an elevated temperature in an inert atmosphere a diester of a dicarboxylic acid with from about 1 to about equivalent proportions of a polyhydroxy compound, in the presence of a catalytic condensing agent selected from the group consisting of those compounds having the formulas:

wherein M represents an alkali metal, M represents an alkaline earth metal selected from the group consisting of magnesium, calcium and strontium, and R represents an alkyl group containing from 1 to 6 carbon atoms.

More specifically, this invention relates to a process for preparing a polyester comprising (A) condensing under substantially anhydrous conditions an aromatic dicarboxylic acid diester having the formula:

wherein Y represents a divalentradical selected from the group consisting of and and

(CHt)n-1OH3 wherein m is a positive integer of from 1 to 5 inclusive, (B) with an alpha,omega-dioxy compound selected from the group consisting of these compounds having the following wherein p represents a positive integer of from 2 to 12 inclusive, R5 and Rs each represents a substituent selected from the group consisting of a hydrogen atom and acyl radical containing from 2 to 4 carbon atoms, R7 represents an alkylene radical containing from 2 to 4 carbon atoms and q represents a positive integer of from 1 to 10 inclusive, the alpha,omega-dioxy compound being employed in such a proportion that there is at least an equivalent amount of alpha and omega oxy substituents in proportion to the carbalkoxy substituents in the overall combination of the aromatic diesters and the alpha,omega-dioxy compounds, (C) in the presence of a condensing agent selected from the group consisting of the novel catalysts set forth are 6,364

above, (D) at an elevated temperature which is increased gradually during the course of the condensation up to a temperature of from about 225 to about 310 C., (E) the condensation being conducted in an inert atmosphere, (F) and conducting the condensation at a very low pressure of the inert atmosphere during the latter part of the condensation. l

Advantageously, the condensing agent is employedin an amount of from about 0.005 %to about 0.2% based on the weight of the aromatic dicarboxylic acid diester. Higher and lower proportionscan also be employed.

Advantageously, the alpha,omega-dioxy compound is employed in such a proportion that there are from about 1.2 to about 3 alpha and omega oxy substituents in proportion to the carbalkoxy substituents in the overall combination of the aromatic diesters and the alpha,omegadioxy compounds. Higher (e. g. and lower (e. g. l) proportions canalso be employed.

Since the alpha, omega-dioxy compounds which can be employed in accordance with this invention are mostadvantageously alpha, omega-dihydroxy compounds and in order to facilitate the phraseology which is employed in this specification, such compounds will hereinafter be, ferred to as polyhydroxy or dihydroxy compounds although it is to be understood that the alpha, omega-dioxy compounds of the typedescribed above are intended to be covered by theterin dihydroxy compounds or the term polyhydroxy herein.

Advantageously, the temperature employed during the earlier part of the condensation is from about 150 to about 220 C. be employed. a Advantageously, the low pressure defined under (F) is less than about mm. of Hg pressure (preferably less than 5 mm.). However, somewhat higher pressures can also be employed.

Higher and lower temperatures canalso Most advantageously, the aromatic dicarboxylic acid' diester is a diester of p,p-sulfonyl dibenzoic acid or terephthalic acid and the polyhydroxy compound 1 is a polymethylene glycol. This invention also includes processes as described above whereby polyesters can be prepared by replacing a part of the described aromatic dibasic acid diester with ,an. ester of a replacement acid which can be an aliphatic 'dibasic acid, e. g. carbonic acid, oxalic aeid, succinic acid,

adipic acid, sebac ic acid, a,a-dirnethylglutaric acid, dimethylamalonic acid, diglycollic acid, p oxydipropionic l acid, -oxydibutyric acid, maleic acid, furnaric acid,

itaconic acid, etc. Similarly, other ester ified acidic modifl fiers can also be incorporatedin conjunction with or in. lieu of these replacement acid esters, e. g. 1ino1eicla cid,

oil,,soybean oil, cota, tonseed oil, tung oil, etc. The process described abovefor.

linolenic acid, fatty acids of linseed the general practice of this invention need not be appreciably modified when such partial replacement acid esters are employed in conjunction with the aromatic dibasic acid esters except when they are unsaturated and tend to form insoluble and infusible products due to cross-linkage effects, in'which event the process described hereinabove is advantageously terminated at an intermediate temperature of about 250 C. before the pressure is reduced whereby products are obtained which can be called soluble intermediate polyesters which are useful in preparing protective coatings. The various polyesters containing replacement acid esters as described in this paragraph can be prepared according to procedures similar to those described in copending applications filed on even date herewith by J. R.

Caldwell, Serial Nos. 313,062 through 313,066.

Polyesters can also be prepared, in accordance with this invention by replacing a part of the described dihydroxy compound with what can be called a polyhydroxy compound which contains 3. or more hydroxy radicals, eLg.

glycerol, sorbitol, pentaerythritol, dipentaerythritol, fi I-Q 2-methyl-2-hydroxymethyl-1,3-propane methylglycerol,

6 diol, 1,2,4-trihydroxybutane, etc. In the preparation of polyesters employing these polyhydroxy compounds, the reaction mixture is not generally heated to the high tern peratures under reduced pressure as described hereinabove since the product would become insoluble and infusible due to cross-linking of the molecules; hence, the process is halted at about 250 C. or less prior to the reduction in pressure of the, inert atmosphere. Various solutions can then be prepared from these soluble polyester products which can then be cast into films or otherwise used in protective coating compositions. In preparing such soluble polyesters it is generally advantageous to employ an unsaturated aliphatic dibasic acid diester in lieu of a part of the described aromatic dibasic acid diesters, e. g. maleic,

fumaric and itaconic diesters. 1 The various polyesters containing replacement polyhydroxy compounds as described in this paragraph can be prepared according to procedures similarto those described in a copending application filed on even date .herewith by J. R. Caldwell, Serial No. 313,069. r

The dihydroxy or polyhydroxy compounds defined above may not actually contain any free hydroxy radicals since they may be in esterified form as indicated by the formulas of the dihydroxy compounds set forth above. However, these hydroxy or substituted hydroxy radicals are referred to generally as hydroxy radicals or substituents. Each diester is considered as containing two carbalkoxy radicals as that term is employed in the definition H of the process as described above since R1 and R4 may be alkyl radicals, or omega-hydroxyalkyl radicals. Even when the process is preceded by the preliminary step described below employing free acids, the term carbalkoxy radicals in the description of the process is intended to encompass such free carboxy radicals.

Furthermore, this invention covers processes as defined above wherein the aromatic dicarboxylic acid diester is formed by a preliminary step comprising condensing an aromatic dicarboxylic acid having the formula:

HOOCR2X--R3-COOH (wherein R2, R3 and X are defined under (A) in the abovedescribed process), with a polyhydroxy compound which is defined above under (B) and is employed in the proportions set forth under (B), at an elevated temperature, after which preliminarystep the novel catalytic condensing agent which is defined under (C) is added and the condensation is completed as defined under (D), (E) and (F); Advantageously, the elevated temperature employed during the preliminary step is substantially that at which reflux conditions subsist; however, higher and lower temperatures can also be used. Advantageously, as indicated hereinbefore, the polyhydroxy compound is em ployed in such a proportion that there are from about 1.2

to about 3 hydroxy substituents in proportion to the acid substituents in the overall combination of the aromatic diester and the polyhydroxy compound. i

In preparing polyesters, especially linear highly polymeric polyesters, it is important to exclude oxygen and moisture at all stages of the condensation, particularly during the latter stages thereof. An inert atmosphere is employed to exclude oxygen; such atmospheres include, hydrogen, nitrogen, helium, etc. The reacting materials employed in the condensation are advantageously substantially anhydrous; however, if water is initially present or is formed during the course of the condensation, it can be substantially completely removed prior to the final stages of the condensation by operating in accordance with the specified process or otherwise.

Examples of aromatic dicarboxylic acid diesters which can be employed as defined above under (A) include the fl-hydroxyethyl diester of'p,p-sulfonyl dibenzoic acid, p,p'-sulfonyl dibenzoic acid dibutyl ester, m,p-sulfonyl dibenzoic acid dipropyl ester, m,m-sulfonyl dibenzoic acid dihexyl ester, methylterephthalate, hexyl terephthalate,

isopropyl terephthalate, as well as various esters having the following formulas:

o -0 can I V 0 04150-0 c-OiiQ-c OOC4H0 CeHnO-QCO-CEh-O-CHQC 0-0 0.1113

onto-o COS(CH1)IS 0,1100 0 7 o-wum-oO-c o-oonz.

011.0-0oO-sO-sO-omo CH:

c I l oirno-o C-ONOO 0-001115 et cetera.

The dihydroxy compounds which can be employed to form highly polymeric linear polyesters are straightchain alkane diols, viz. polymethylene glycols, wherein the hydroxy radicals are positioned at the two ends of the alkylene'chain. Examples of such glycols include ethylene glycol, 1,3-propylene glycol,'1,4-butylene glycol, l,6-hexylene "glycol, l,l0-decamethylene glycol, 1,12 dodecamethylene glycol, etc. As indicated above, mono or diesters of these glycols can also be employed. Thus, the acetates, 'propionates and butyrates are examples of such esters. The'defined ether glycols can be employed either in lieu of the polymethylene glycols or in conjunctiontherewith, as'rnodifiers. Examples of ether glycols include diethylene glycol, triethylene glycol, tetraethylene glycol, bis (4-hydroxybutyl) ether, bis (3-hydroxypropyl). ether, etc.

Valuable. fibers can be advantageously prepared employing .the highermeltingpolyesters, which can be pro-J tilled-rapidly and the ester interchange was practically duced according to the procedures described herein. Preferably no aliphatic ether glycol ,is employed when fibers are to be prepared. Furthermore, the aromatic acid diesters should ordinarily contain only p, p linkages when highly polymeric linear polyesters are desired. However, on the other hand, valuable polyesters can be prepared employing aliphatic ether glycols without any polymethylene glycol although the product obtained will not be suitable for forming useful fibers. plies to the employment of aromaticdiesters containing linkages in other than the para positions.

The catalytic condensing agents which can be employed havebeen described above. From about 0.005% to about 0.2% of such catalysts based on the weight of thediesters being condensed can be employed. Higher or lower percentages can also be employed. Generally, from about 0.01% to about 0.06%-0f the catalytic condensing agent can be advantageously employed, based on the Weight of the various diesters being condensed.

The temperature at which polyesterification can be conducted is dependent upon the specific reactants involved in} any given reaction. In general, the reaction mixture can be heated with-agitation at from about 150 to about 2 20fCQ for from approximately one to three hours in an inert atmosphere (e. g. nitrogen or hydrogen); the mixture can then be heated with agitation at from about 225'24'0, to about 280-.3l0.. C. in the same atmosphere for approximately 1 .to 2 hours. Finally, the pressure can be greatly reduced to form a vacuum (less than about 1-5 mm. of Hg pressure but preferably on the order of less than 5 mm. of Hg pressure.) while the temperature is maintained in the same range (225 310 0.); these conditions are advantageously maintained for approximately 1 to 6 additional hours. This final phase is advantageously' carried out with good agitation under the high vacuuinin order to facilitate the escape of volatile products from the highly viscous melt. The conditions can be varied considerably depending upon the degree of polyesterification desired, the ultimate properties sought, thestability of the polyester being produced, and the use for which the product'is intended.

The reaction can be carried out in the presence or absence of a solvent. Inert, high boiling compounds, such as diphenyl ether, 'diphenyl, mixed tolyl sulfones, chlorinated. naphthalene, chlorinated diphenyl, dimethyl sulfolane, etc., can be usedas the'reaction medium.-

vIn the examples given below, the hot bar sticking temperatureisreferred to in several'instances. The 'hot bar sticking test .can be briefly described as follows: A polyester fiber is placed on the fiat surface of a heated bar and a weight of grams is applied to the fiber along .a distance of /8 inch of the fiber length. The contact surface of this weight has acoating of polytetrafiuoroe'thylene' which acts as a thermal insulator. The fiber is allowed to remain in contact with the bar under this weight for one 'minute. The minimum 'ternperature at which the'fiber adheres to the hot bar under these conditionsis the sticking temperature as that term is employed in the examples given herein.

' This inventioncan be further illustrated by the following examples; in addition to these examples it is apparent that other variations and modifications thereof can be adapted to obtain similar results:

Example 1.NaH(Zr(OC4H9)s) as the catalyst were placed in a vessel equipped with a variable speed.

stirrer of the anchor type, a short distillation column, and a gas inlettube for purified hydrogen. Two cc. of n-butyl alcohol containing 0.01 g. of NaH(Zr(OC4H9)e) were added. The mixture was heated in a metal bath at 200- 210 C; and stirred at 100-120 R. P. M. while pure hydrogenwas passed over the surface. Butyl alcohol dis The same ap complete in 30 minutes. The temperature was then raised to270280 C. in 15 minutes and heating continued'for l15 minutes. Some of the excess glycol distilled off at this stage. The hydrogen gas was shut off, and a vacuum of about 1 mm. of Hg pressure applied. The melt rapidly increased in viscosity and in about 15 minutes it was necessary to reduce the stirrer speed to -40 R; P. M. As the viscosity increased, the stirrer speedwas gradually reduced. After a total time of 30-40-minutes under vacuum, the melt had become too viscous to stir and the reaction was stopped. The melt obtained was clear and colorless. After cooling slowly, the product was hard and opaque, due to crystallinity. If the melt is suddenly cooled or quenched, it has a tendency to remain amorphous and transparent. On a hot stage,in polarized light, the crystalline material shows a melting point of 270- 280 C. The inherent viscosity in 60% phenol-40% tetrachlorethane is 0.70-0.80. Fibers can be pulled from the melt and cold-drawn 500-600%. They stick on a ihotzbar at 230-240 C. The polyester also gives valuable sheets and films.

One hundred grams p;p"-sulfonyldibenzoic.acid ethyl ester and 40 g. 1,5-pentanediol were placedtina reaction vessel equipped with .a stirrer, la short distillation column .and an inlet tube for purified nitrogen. .:F.iv.e .cc. ofaethyl alcohol containing 0.4 g. of KH(Zr(OC2I-I5)s)-was :added and :the mixture heated at 180-200 C. with stirring. After'l hour, the distillationiof ethyl alcoholsceased, :and the temperature was raised to 280285 C. where it was held for 20 minutes. A vacuum of 0.5 to 110 mm. was applied for 1 hour, while the temperature was maintained at 280285 C. A colorless product :having an inherent viscosity of 0.80-0.90 in 60% phenol-40% tetrachlorethane solution was -obtained. Fibers pulled from the melt andcold drawn 4005'00% :ShOWJQ. sticking temperature of 240-2S0 C. The product is also auseful for films and sheets.

Example 3.Mg(Zr(OCzHs)s) as the catalyst One gram mol of methyl sebacate, 4 gram mols of p,p'-sulfonyl-dibenzoic acid butyl ester, and 7 gram mols 1,6-hexanediol were placed in a vessel as described in Example 2. Five-hundredths percent Mg(Zr(OC 2"H5)s) was added, based on the weight of the two esters. A heating schedule similar to that given in Example 2 was followed. The product obtained is very tough and rubbery. Ithas an inherent viscosity of 0.80ina solventof 60% phenol-40% tetrachlorethane. Fiberspulled from the melt show a rubbery elastic elongation -of30 40%. This product is also useful as a molding plastic;

One gram mol of methylisophthalate, 5 gram mols of p, p'-sulfonyl-dibenzoic acid ethyl ester, and 10-grammols 1,5-pentanedibl were placed in a vessel as described in Example 2. Six-hundredths percent MgQHZr(OC4I-*Is)s)z was added, based on the weight of the two esters. A heating schedule similar to that given in Example 2 was followed. The product obtained is hard and crystalline; It is usefulfor injection molding. 3

Example 5 .Ca(HZr OCHs s) 2 as the catalyst One hundred grams ofmethylterephthalateand 40 g. of ethylene glycol were placed in avesselas described in Example 1. Three-hundredths percent [CQtHZ/RQOQHSDQZ was added, based on the weight of methylterephthalate. A heating schedule was followed as described in Example l. A polyester having excellent color and an inherent viscosity of 0.80-0.90 was obtained.

Example 6.Sr(HZr(OC3H5)s)2 as the catalyst The polyester described in Example 5 was prepared again by the same process employing the same apparatus; however, the catalyst was 0.03% of Sr(HZr(OC3H5)s)2 in in lieu of the corresponding Ca salt employed in ample 5. The product obtained has thesame properties of the'polyester described in Example 5.

Example 7..-LiI-.I (-Zr(OC5H11.).s.) as the catalyst The polyester described in Example 2 was once again prepared employing the same ,apparatus and process except for the substitution of 0.4 gram of LiH(Zr(OC5Hi1)s) as the catalyst. The polyester obtained had the same properties as that described under Example 2.

Example 8.-N3H(ZI(OC4H9)6) as the catalyst One gram mole of p,p-dicarbethoxydiphenyl methane and ;2.1 gram :moles of ethylene glycol were condensed in apparatus as described in Example ll according .to the procedure set forth therein employing 2 cc. of the same catalyst solution. The product obtained was a highly polymeric linear polyester useful as a molding resin, for preparing films, sheets, etc.

Example'9.--NaH(Zr(OC4Hg).6 as the catalyst One gram mole of .p,p-dicarbomethoxybenzophenone and 2.4 gram moles of trimethylene glycol .Were condensed in apparatus as described in Example 1 according to the procedure set forth therein employing 2 cc. of the same catalyst solution. The ,producnobtained was a highly polymeric linear polyester useful as a molding resin, for preparing films, sheets, etc.

Example l0.NaH(Zr-(:OC4Hs.)s) as thevcatalyst N,N bis(p earbohexoxyphenyDmethylanrine, condensed with ethylene glycol, tetramethylene glycol and hexameth- 'ylene glycol.

In the various formulas given for the catalysts in the above examples, -C4H9 and the formulas for other such alkyl radicals are intended to represent the straight chain alkyl radicals. However, branched chain radicals can alsobe employed.

Example 11..- .K;2Zr(OCiH9)s ,as the catalyst The polyester described in Example 1 was prepared again by the same process employing the same apparatus; however, the catalyst was-0.04% of K2Zr(OC4H9)e in lieu of the NaHZr(OC4I-I )s employed .in Example 1. The product obtained has the same properties as the polyester described in Example 1.

Example ,l2.-CaZr('OCH3 )s .as the ,catalyst The polyester described in Example 5 was prepared again "by the same process employing the same apparatus; however, the catalyst was 0.05 of CEIZ'IOCHIQG in-lieu of the corresponding acid salt employed in Example 5 The 'produc't'obtained has the same fPIOPBI'ilES as the polyester describedin Example 5.

We claim:

l. A' processfor preparing a polyester comprising (A) condensing under substantiallyanhydrous conditions an aromatic dicarboxylic acid diester having the formula:

wherein R1 and R4 each represents a substituent selected from the group consisting of an alkyl radical containing from 1 to 10 carbon atoms and an omega-hydroxyalkyl radical containing from 2 to 12 carbon atoms, R2 and R3 each represents (CH2)111 wherein n is a positive integer of from 1 to 5 inclusive, and X represents a divalent 11 aromatic radical selected from the group consisting of those having the following formulas:

and

wherein Y represents a divalent radical selected from the group consisting of wherein p represents a positive integer of from 2 to 12 inclusive, R5 and R6 each represents'a substituent selected from the group consisting of a hydrogen atom and an acyl radical containing from 2 to 4 carbon atoms, R'z represents an alkylene radical containing from 2 to 4 carbon atoms and q representsa positive integer of from 1 to inclusive, the alpha, omega-dioxy compound being employed in such a proportion that there is at least an equivalent amount of alpha and omega oxy substituents in proportion to the carbalkoxy substituents inthe overall combination of the aromatic diester and the alpha, omegar-dioxy compound, (C) in the presence of a catalytic condensing agent selected from the group consisting of those compounds having the following formulas:

and

M(Zr(OR)s) wherein M represents an alkali metal, M represents an alkaline earth metal selected from the group consisting of magnesium, calcium and strontium, and R represents an alkyl group containing from 1 to 6 carbon atoms, (D) at an elevated temperature which is increased gradually during the course of the condensation upto a temperature of from about 225 to about 310 C., (E) the condensation being conducted in an inert atmosphere, (F) and conducting the condensation at a very low pressure of the inert atmosphere during the latter part of the condensation.

2. A process as defined in claim l'wherein the con- ,densing agent is employed in an amount of from about 0.005% to about 0.2% based on the weight of the aromatic dicarboxylic acid diester.

3. A process as defined in claim 2 wherein the alpha,- omega-dioxy compound is employed in such a proportion that there are from about 1.2 to about 3 alpha and omega 7 9X3! substituents in proportion to the carbalkoxy substituents in the overall combination of the aromatic diester and the alpha, omega-dioxy compound.

4. A process as defined in claim 3 wherein the elevated temperature employed during the earlier part of the condensation is from about C. to about 220 C.

5. Aprocess as defined in claim 4 wherein the low pressure defined under (F) is less than 15mm of Hg pressure.

6. A process as defined in claim 5 wherein the low pressure defined under (F) is less than 5mm of Hg pressure.

7. A process as defined in claim 6 wherein the aromatic diester is derived from p,p-sulfonyl dibenzoic acid and the condensing agent is NaH(Zr(OC4H9)e).

8. A process as defined in claim 6 wherein the aromatic diester is derived from p,p-sulfonyl dibenzoic acid and the condensing agent is KH(Zr(OC2H5)s).

9. A process as defined in claim 6 wherein the aromatic diester is derived from p,p-sulfonyl dibenzoic acid and the condensing agent is Mg(Zr(OC2H5)6).

10. A process as defined in claim 6 wherein the aromatic diester is derived from p,p'-sulfonyl dibenzoic acid and the condensing agent is Mg(HZr(OC4H9) s)2.

11. A process as defined in claim 6 wherein the aromatic diester is derived from terephthalic acid and the condensing agent is Ca(HZr(OCH3) s)2.

12. A process as defined in claim 1 wherein the aromatic dicarboxylic acid diester is formed by a preliminary step comprising condensing an aromatic dicarboxylic acid having the formula:

wherein R2, R3, and X are defined under (A), with an alpha, omega-dioxy compound which is defined under (B) and is employed in the proportions set forth under (B), at an elevated temperature, after which preliminary step the catalytic condensing agent which is defined under (C) is added and the condensation is completed as defined under (D), (E) and (F). r

13. A process as defined in claim 12 wherein the elevated temperature employed during the preliminary step is substantially that at which reflux conditions subsist, and the condensing agent is employed in an amount of from about 0.005% to about 0.2% based on the weight of the aromatic dicarboxylic acid diester, the alpha, omega-dioxy compound is employed in such a proportion that there are from about 1.2 to about 3 alpha and omega oxy substituents in proportion to the acid substituents in the overall combination of the aromatic diester and the alpha, omega-dioxy compound, the elevated temperature employed during the earlier part of the condensation to form the polyester is from about 150 C. to about 220 C., the low pressure defined under (F) is less than about 15 mm of Hg pressure and all materials employed in the process are substantially anhydrous.

References Cited in the file of this patent Meerwein: Ann. 455, 227, 1927. Meerwein: Ann., 476, 113, 1929. 

1. A PROCESS FOR PREPARING A POLYESTER COMPRISING (A) CONDENSING UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS AN AROMATIC DICARBOXYLIC ACID DIESTER HAVING THE FORMULA 